1. Field of the Invention
This invention concerns the improvement of the maneuverability of an aircraft during the approach to landing and then flare-out phases with the aid of an appropriate control of the spoiler flaps, also called air brakes.
2. Discussion of the Background
By “improving the maneuverability of an aircraft” one understands here that which facilitates its operation.
The main portion of approaches to landing, with respect to commercial aircraft is carried out under a classic flight path angle γ of −3° approximately.
In reference to FIG. 5, please note that the flight path angle γ corresponds to the angle between the velocity vector V of the center of gravity C of the aircraft and the horizon H.
The trim θ is the angle between the axis A of the aeroplane A and the horizon H, and the angle of incidence α the angle between the axis A of the aircraft and the velocity vector V. The relationship connecting these various angles is the following:θ=α+γ.
Generally speaking, the aerodynamic configuration of an aircraft is modifyable in particular with the aid of air brakes, flaps and leading edge slats.
In an approach-to-landing phase at the so-called classic angle in the order of γ=−3°, the aerodynamic configuration of an aircraft results from the air brakes being retracted, the flaps being deployed and the leading edge slats being deployed. Such an aerodynamic configuration, in association with a given approach velocity, forces the aircraft to fly at a certain angle of incidence and hence at a certain pitch. Since most approaches in view of a landing are carried out with a classic flight path angle of −3°, pilots are in the habit of performing every time the same landing with angles of incidence and of pitch that are essentially similar at each landing. Since during the landing phase the pilot cannot divert his attention by checking the flight path angle and incidence gauges, he evaluates, to some extent, the behavior of the aircraft according to the pitch, by observing the attitude of the aircraft with respect to the outside environment.
The development of certain airports located in urban areas as well as efforts related to aircraft noise reduction have led to the appearance of new specific approach procedures. Such specific approach procedures continue to impose flight path angles that are superior (as absolute value) to the classic flight path angle of −3°. Typically these specific approach angles, also known as steep angle approaches, have values below −4.5°.
In order to maintain the required flight path angle, while keeping the velocity of the aircraft constant during the approach to landing, a specific drag/thrust balance must be obtained. A large majority of airplanes operating in this kind of approach are equipped with pusher type airscrews. This type of motorization allows, due to the orientation of the airscrews, to obtain the necessary lift to drag ratio to follow the required flight path angle.
For airplanes equipped with turbojet engines, it is necessary to make use of aerodynamic tricks in order to achieve the necessary lift to drag ratio.
On certain aircraft spoilers (or air brakes) are used. The air brakes constitute aerodynamic control surfaces, generally installed on the top side of the wings, behind their structural chassis and ahead of the trailing edge flaps on which rest their own trailing edges.
Under the action of actuators, for instance hydraulic, electrical or mechanical jacks which are themselves controlled for instance by a lever operated by the pilot of the aircraft, said air brakes may assume:                either a retracted position for which they are lodged in the top side of the corresponding wing, ensuring the aerodynamic continuity of said top side of the wing;        or one or the other of the deployed positions for which they jut out from the top side of the corresponding wing, being inclined in relation to said top side of the wing.        
Thus, in the retracted position said air brakes are integrated into the aerodynamic profile of the top sides of the wings of the aircraft. Whereas for each of the deployed positions, each of which is associated with a specific function and is defined by a value of the control surface angle in relation to the corresponding wing top side, said air brakes produce diminished lift and increased drag the amplitudes of which depend on said control surface angle and of the surface of said air brakes.
These air brakes may be used for different purposes such as:                reduction of the velocity of the aircraft at the end of the landing phases and possibly the abortion of the take-off.        reduction of the velocity of the aircraft in flight or increase of the flight path angle of said aircraft;        adhesion of the aircraft to the ground to improve braking during the landing or take-off aborting phases;        on approach at the classic flight path angle (−3°), automatic coupling (continuous oscillation) of the deflection of the aircraft with reference input (pitch of the aircraft in relation to the trajectory of descent, altitude, vertical speed) depending on the deviation of the reference input from the actual position of the aircraft (U.S. Pat. No. 3,589,648);        in-flight control of the wing-over [or rolling] of the aircraft by acting asymmetrically on the air brakes of the two wings;        generation of a yawing moment by asymmetric action on the air brakes of the two wings participating in countering the effects of an engine failure during take-off; or        aid in diminishing the fixed end wing/fuselage moment at the heavy load factors (maneuvers, wind gusts), by modifying the distribution of lift along the wings.        
So, the functions performed by the air brakes are varied.
By diminishing the ratio of lift to drag, deflecting the air brakes allows also to increase the angle of descent at a given speed. This is already being used in the event of a sudden decompression of the aircraft, obliging the pilot to descend to an altitude where the passengers are able to breathe the ambient air without [oxygen] masks.